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Re: setting up postscreen on a system with multiple external interfaces

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  • Erik Slagter
    ... Yes I blame the documentation, but not the software. I ve been using postfix for, well, something like ten years or more, I think it s the best thing since
    Message 1 of 25 , Feb 21, 2013
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      On 21-02-13 19:17, DTNX Postmaster wrote:

      > You keep blaming the documentation and the software, when the problem
      > is most likely in your understanding of it.

      Yes I blame the documentation, but not the software. I've been using
      postfix for, well, something like ten years or more, I think it's the
      best thing since sliced bread, especially compared to sendmail, qmail
      and exchange.

      The way I've configured it now, really suits the demands. I cannot
      remember any phrases in the documentation recommending not to do it this
      way (i.e. start multiple smtp listeners on different addresses with
      different options, in one master process). If it actually appears to be
      disrecommended, then that's clear to me, no problem.

      > Simplify your configuration. Don't assume that what goes for 'smtpd'
      > goes for 'postscreen' as well.

      I'd like to, but where do I find what I CAN assume? The factual
      documentation of postscreen is so sparse, it's mostly HOWTO,
      monkey-see-monkey-do.

      > Pick sensible defaults for 'main.cf',
      > and override only the options that are absolutely necessary.

      That's already done.

      > If you have a legitimate reason (as in, contractual obligations or
      > whatnot) to require seperate hostnames, greetings, TLS settings and
      > such, use the multi-instance features and seperate them. Otherwise the
      > KISS principle applies.

      Actually this way is much more KISS to me than running multiple
      instances of "master".

      I'm starting to think that the reason this operation is not documented,
      is because it's not possible. It looks like the postscreen layer
      literaly sits between the remote client and the smtp process, and the
      information where the connection took place (interface/address) is not
      available at the point where the smtpd is invoked.

      If that's the case, postscreen is not the way to go for me. I assumed
      postscreen was implemented a bit like proxy-filter, where you can run
      any number of filters on any number of addresses.
    • Erik Slagter
      ... I m just following the REPORT A PROBLEM procedure I was kindly pointed at... ... Yes at this point the smtpd/master has no knowledge of the
      Message 2 of 25 , Feb 21, 2013
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        On 21-02-13 19:30, Noel Jones wrote:

        > You've shared too much. By now no one has any idea what you're doing.

        I'm just following the "REPORT A PROBLEM" procedure I was kindly pointed
        at...

        > When postscreen decides to pass the connection to smtpd, postscreen
        > is no longer involved, and smtpd has no knowledge of what transpired
        > between postscreen and a client.

        Yes at this point the smtpd/master has no knowledge of the
        interface/address, that's exactly the thing I fear.

        > At some point you reported:
        > [ .. ]
        >> -o postscreen_tls_security_level=may
        >> -o tlsproxy_tls_security_level=may
        >
        > both these belong in main.cf, or better, set main.cf:
        > "smtpd_security_level = may" and leave these at their defaults.

        Tried both, doesn't matter. The thing is that what way you set the smtpd
        options (in main.cf) you cannot override them with postscreen. So if you
        set the default value suitable for address a and b, they must be
        override for address c and d and vv. Yes, I have some internal address
        that need to have tls_security=none and yes, that works like a charm
        without postscreen enabled.

        >> -o postscreen_cache_map=btree:$data_directory/postscreen_cache-ipv4
        >
        > The cache map parameter belongs in main.cf. Probably a mistake to
        > create separate caches.

        Nope, the cache map cannot be shared between two smtpd processes (see
        documentation ;-)). It's not a problem though, because one db holds ipv4
        addresses and the other is ipv6 addresses.

        > For the TLS part, it will be much easier to turn TLS on in main.cf,
        > then turn it off on the interfaces where you don't want to offer it
        > with "-o smtpd_tls_security_level=none".

        All relevant options for tls are actually set in main.cf. It's only that
        it's not enabled there, it's enabled on a per-address base. Which works.

        > For the greeting banners, set them as macros in main.cf and then
        > refer to them by $name in master.cf

        That's a possibility, but it's not necessary and doesn't solve the problem.

        > Now tell postscreen which ports to listen on and to enable the banner:
        >
        > # master.cf
        >
        > mx1.ipv4.slagter.name:smtp inet n - n - 1 postscreen
        > -o postscreen_greet_banner=$postscreen_greet_v4
        >
        > mx1.ipv6.slagter.name:smtp inet n - n - 1 postscreen
        > -o postscreen_greet_banner=$postscreen_greet_v6
        >
        > Next we tell smtpd to get it's connections from postscreen.
        > On your existing "smtp ... smtpd" entries where you want postscreen,
        > change the "smtp inet n" part to "smtp pass -"
        > This is described in detail in
        > http://www.postfix.org/POSTSCREEN_README.html#config
        >
        > so your existing entry:
        >> mx1.ipv4.slagter.name:smtp inet n - n - 2 smtpd
        >
        > would become:
        > mx1.ipv4.slagter.name:smtp pass - - n - 2 smtpd

        I get your drift, but IIRC I already tried this (multiple times, with
        slight variations) and also reported about the outcoming of that:
        "fatal: address already in use".

        Did I already mention I have followed all the steps from the README as
        closely as possible?
      • Viktor Dukhovni
        ... Take a DEEP breath, relax and don t *try* implementing new configurations you don t yet understand. The shots in the dark will just get you more confused.
        Message 3 of 25 , Feb 21, 2013
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          On Thu, Feb 21, 2013 at 05:46:26PM +0100, Erik Slagter wrote:

          > Another variation I tried ("pass" and "postscreen" the other way
          > around). This works, but gives the original problem, the smtpd
          > options are not honoured (especially banner and starttls="may"),
          > even though I set both:

          Take a DEEP breath, relax and don't *try* implementing new
          configurations you don't yet understand. The shots in the dark will
          just get you more confused.

          It is time to try to *understand*.

          1. A running Postfix instance is a collection of separate background
          services (daemons) launched by an inetd-like service supervisor known
          as "master. These services run independently in separate processes
          and communicate with each other using unix-domain sockets.

          They are configured either via main.cf (best practice) or via
          master.cf "-o parameter=$value" overrides (when you must).

          The MOST important thing you need to understand about this is:

          Adding "-o FOO=BAR" to the master.cf entry for SERVICEA has
          NO EFFECT on the value of FOO in SERVICEB!

          Even when the MESSAGE is passed from SERVICEA to SERVICEB the
          parameter settings ARE NOT.

          Thus when you convert an existing "smtpd" entry to a "postscreen"
          entry, it is a grave mistake to leave the "smtpd" (-o options)
          that tune the functionality of smtpd attached to the "postscreen"
          service. It (postscreen) won't care and the destination "smtpd"
          to which the message is handed off will no longer know the parameters.

          2. To provide multiple smtpd personalities, you need to implement multiple
          "smtpd" services each with their own settings. (As you do when smtpd
          listens directly on an "inet" socket).

          3. To implement 2. with postscreen, each "inet" listening postscreen
          (with settings relevant for postscreen) must hand the message off
          to an "smtpd" appropriate for its listening IP address.

          4. Therefore, you need multiple "smtpd" "pass" services for "postscreen"
          to hand the connection to. The postscreen(8) manual page refers you to

          http://www.postfix.org/postconf.5.html#smtpd_service_name

          which must specify the service name of a "pass" entry in master.cf,
          you need one of these for each distinct postscreen instance.

          192.0.2.1:25 inet ... postscreen
          -o smtpd_service_name=25@192.0.2.1
          -o <postscreen-related-settings> ...
          25@192.0.2.1 pass ... smtpd
          -o <smtpd-related-settings> ...

          Lather, rinse, repeat:

          192.0.2.1:587 inet ... postscreen
          -o smtpd_service_name=587@192.0.2.1
          -o <postscreen-related-settings> ...
          587@192.0.2.1 pass ... smtpd
          -o <smtpd-related-settings> ...

          Lather, rinse, repeat:

          192.0.2.2:25 inet ... postscreen
          -o smtpd_service_name=25@192.0.2.2
          -o <postscreen-related-settings> ...
          25@192.0.2.2 pass ... smtpd
          -o <smtpd-related-settings> ...

          Lather, rinse, repeat:

          192.0.2.3:25 inet ... postscreen
          -o smtpd_service_name=25@192.0.2.3
          -o <postscreen-related-settings> ...
          25@192.0.3.2 pass ... smtpd
          -o <smtpd-related-settings> ...

          ... but do stop eventually ... :-)

          --
          Viktor.
        • Erik Slagter
          ... And THAT is exactly the clue I was looking for! It works! The only thing that would have to be in the README file is the need to use smtpd service names
          Message 4 of 25 , Feb 22, 2013
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            On 21-02-13 20:07, Viktor Dukhovni wrote:

            > [ ... ] (lot of patronising text removed)

            > 4. Therefore, you need multiple "smtpd" "pass" services for "postscreen"
            > to hand the connection to. The postscreen(8) manual page refers you to
            >
            > http://www.postfix.org/postconf.5.html#smtpd_service_name
            >
            > which must specify the service name of a "pass" entry in master.cf,
            > you need one of these for each distinct postscreen instance.

            And THAT is exactly the clue I was looking for! It works!

            The only thing that would have to be in the README file is the need to
            use "smtpd service names" in case of multiple smtp listeners, point to
            http://www.postfix.org/postconf.5.html#smtpd_service_name and then add a
            bit of really helpful text to the current one:

            "The internal service that postscreen(8) hands off allowed connections
            to. In a future version there may be different classes of SMTP service."

            If you google for this command, you'll get references to either this
            text or this thread :-(

            So for other people seeking to do the same, this does the trick, it's
            also simple once you know, the "service" parameter of a "pass" service
            is not an address:portno combo but an identifier:

            #
            # outside -> inside
            # postfix(25) -> amavis(10025)
            #

            mx1.ipv4.slagter.name:smtp inet n - n - 1 postscreen
            -o postscreen_cache_map=btree:$data_directory/postscreen_cache-ipv4
            -o
            postscreen_greet_banner=mx1.slagter.name-ESMTP-mx1-postscreen-1-ppp0-ipv4-25
            -o smtpd_banner=mx1.slagter.name-ESMTP-mx1-postscreen-2-ppp0-ipv4-25
            -o postscreen_tls_security_level=none
            -o smtpd_service_name=mx1_ipv4

            mx1_ipv4 pass - - n - - smtpd
            -o myhostname=mx1.slagter.name
            -o smtpd_banner=mx1.slagter.name-ESMTP-$mail_name-mx1-ppp0-ipv4-25
            -o smtpd_tls_security_level=may
            -o smtpd_proxy_filter=nemesis.ipv4:10025 # amavis

            mx1.ipv6.slagter.name:smtp inet n - n - 1 postscreen
            -o postscreen_cache_map=btree:$data_directory/postscreen_cache-ipv6
            -o
            postscreen_greet_banner=mx1.slagter.name-ESMTP-mx1-postscreen-1-ppp0-ipv6-25
            -o smtpd_banner=mx1.slagter.name-ESMTP-mx1-postscreen-2-ppp0-ipv6-25
            -o postscreen_tls_security_level=none
            -o smtpd_service_name=mx1_ipv6

            mx1_ipv6 pass - - n - - smtpd
            -o myhostname=mx1.slagter.name
            -o smtpd_banner=mx1.slagter.name-ESMTP-$mail_name-mx1-ppp0-ipv6-25
            -o smtpd_tls_security_level=may
            -o smtpd_proxy_filter=nemesis.ipv4:10025 # amavis
          • Viktor Dukhovni
            On Fri, Feb 22, 2013 at 11:04:34AM +0100, Erik Slagter wrote: First, a quick comment, all of the sturm and drang in this thread is the result of a peculiar
            Message 5 of 25 , Feb 22, 2013
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              On Fri, Feb 22, 2013 at 11:04:34AM +0100, Erik Slagter wrote:

              First, a quick comment, all of the sturm and drang in this thread
              is the result of a peculiar reluctance of most users to heed the
              advice in MULTI_INSTANCE_README and simplify their configurations
              by handling each distinct message flow in a separate Postfix
              instance, each of which can be configured with few if any master.cf
              tweaks, and understood and maintained much more easily.

              A combination of MULTI_INSTANCE_README and POSTSCREEN_README would
              get you there much more quickly, and even allow simpler configuration
              of cases where identical policies apply to multiple protocol:address
              endpoints, since you can just set inet_interfaces in main.cf to list
              one or more network addresses for a given instance.

              I strongly recommend that you take the time to refactor your
              configuration to separate each flow into its own queue. The initial
              investment of time pays off quickly in easier to manage configurations
              and operational support (e.g. separate queues make it easier to
              see which flow is having problems).

              > On 21-02-13 20:07, Viktor Dukhovni wrote:
              >
              > > [ ... ] (lot of patronising text removed)

              Text that is required background knowledge to understand what
              follows, misconstrued to be patronizing rather than emphatic. Chill
              man, the blustery tone of this thread is mostly the result of your
              reticense to (AFAIK you never did) post the actual master.cf
              configuration that failed to meet your expectations. You should
              probably also not have included the text below in the initial post:

              The options (-o) that I specify on the various per-interface
              smtpd instances are NOT honoured anymore. ...

              Is this intentional? A know[n] bug? ...

              I must say the "howto" isn't very clear on this matter, it assumes you
              only have only one external interface.

              This is rude to the developers who take great pains to make Postfix
              unusually robust and well documented. The "patronising" text is
              sufficient to logically deduce that (and why) you need multiple
              smtpd "pass" services, at which point one looks for a parameter to
              specify the pass service, and finds it (in this case clustered
              sub-optimally with unrelated settings, we'll fix that) in the postscreen(8)
              manpage.

              If Wietse is still reading this, we should move "smtpd_service_name"
              to its ownn section nearer the top of the postscreen(8) manpage.

              Fortunately, the parameter name is just what you'd expect if you've
              ever seen "cleanup_service_name" which plays the same role one
              handoff downstream.

              > >4. Therefore, you need multiple "smtpd" "pass" services for "postscreen"
              > > to hand the connection to. The postscreen(8) manual page refers you to
              > >
              > > http://www.postfix.org/postconf.5.html#smtpd_service_name
              > >
              > > which must specify the service name of a "pass" entry in master.cf,
              > > you need one of these for each distinct postscreen instance.
              >
              > And THAT is exactly the clue I was looking for! It works!

              Naturally, since it is simply a logical consequence of understanding
              the patronising text. :-) Perhaps some people even spotted the
              transposition error in the last "Lather, rinse, repeat" example.
              (It has been observed that students pay more attention to technical
              books that contain minor errors that require them to pause and
              think, and that they learn more from these than from polished
              material that requires less attention).

              [
              Plus the fact that "unix" and "pass" service names are just file
              names in /var/spool/postfix/private/ which I started to describe
              in my first post, but decided to keep it more concise in the hope
              that this will be apparent from context.

              The master.cf services live in one of three namespaces:

              - inet/public (inet can't be private).

              - unix/public

              - unix/private

              Each of the "unix" cases subsumes "unix", "fifo" and "pass" since these
              all are accessed via paths in /var/spool/postfix/{public,private}.

              All delivery agents are "private" while "pickup", "qmgr", "flush"
              and "showq" are "public" to support postdrop(1) and postqueue(1)
              and their sendmail(1) interfaces. Almost everything else is private,
              except for cleanup(8) which AFAIK is public only for historical
              reasons.
              ]

              --
              Viktor.
            • Wietse Venema
              ... This was changed from private into public , so that postdrop could directly submit mail into cleanup, using the maildrop directory only as a fall-back
              Message 6 of 25 , Feb 22, 2013
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                Viktor Dukhovni:
                > All delivery agents are "private" while "pickup", "qmgr", "flush"
                > and "showq" are "public" to support postdrop(1) and postqueue(1)
                > and their sendmail(1) interfaces. Almost everything else is private,
                > except for cleanup(8) which AFAIK is public only for historical
                > reasons.

                This was changed from "private" into "public", so that postdrop
                could directly submit mail into cleanup, using the maildrop directory
                only as a fall-back mechanism in case cleanup transaction failed.
                Recovering from all possible failure modes is complicated and I did
                not get around to write that code (and there are few people who I
                would trust to write it).

                Wietse
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